1. Field of the Invention
The present invention relates to an oxide catalyst for use in catalytic oxidation or ammoxidation of propane or isobutane in the gaseous phase. More particularly, the present invention is concerned with an oxide catalyst for use in a catalytic oxidation or ammoxidation of propane or isobutane in the gaseous phase, which comprises an oxide represented by the following formula (I):Mo1VaNbbXcYdZeQfOn  (I)wherein X is at least one element selected from the group consisting of tellurium and antimony; Y is at least one element selected from the group consisting of aluminum and tungsten; Z is at least one element selected from the group consisting of elements which individually form an oxide having a rutile structure; Q is at least one element selected from the group consisting of titanium, tin, germanium, lead, tantalum, ruthenium, rhenium, rhodium, iridium, platinum, chromium, manganese, technetium, osmium, iron, arsenic, cerium, cobalt, magnesium, nickel and zinc; and a, b, c, d, e, f and n are, respectively, the atomic ratios of vanadium (V), niobium (Nb), X, Y, Z, Q and oxygen (O), relative to molybdenum (Mo), and wherein: 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦0.5, 0≦e≦3, 0≦f≦9, with the proviso that 0<d+e≦3.5, and n is a number determined by and consistent with the valence requirements of the other elements present in the oxide of formula (I). By the use of the oxide catalyst of the present invention for the catalytic oxidation or ammoxidation of propane or isobutane in the gaseous phase, it becomes possible to improve the selectivity for the desired unsaturated carboxylic acid or unsaturated nitrile and to conduct an efficient production of the desired product. By virtue of these properties, the oxide catalyst of the present invention can be advantageously used in various industrial fields. The present invention is also concerned with a process for producing an unsaturated carboxylic acid or an unsaturated nitrile by using the above-mentioned oxide catalyst.
2. Prior Art
Acrylic acid and methacrylic acid (each of which is an unsaturated carboxylic acid), as well as acrylonitrile and methacrylonitrile (each of which is an unsaturated nitrile) are very important compounds in the industries. With respect to the method for producing these compounds, there is a well-known method in which propylene or isobutylene (each of which is an alkene (olefin)) is subjected to catalytic oxidation or catalytic ammoxidation in the gaseous phase to thereby obtain a corresponding unsaturated carboxylic acid or unsaturated nitrile.
Recently, attention has been attracted to a technique in which propane or isobutane (each of which is an alkane) is used as a substitute for the above-mentioned alkene. Specifically, an alkane is subjected to catalytic oxidation or catalytic ammoxidation in the gaseous phase to thereby produce a corresponding unsaturated carboxylic acid or unsaturated nitrile. A number of proposals have been made with respect to the methods for utilizing such a technique and the catalysts for use in such methods.
For example, EP 767164B, Unexamined Japanese Patent Application Laid-Open Specification Nos. 10-28862, 10-330343, 11-57479 and 11-226408, U.S. Pat. Nos. 6,036,880, 5,231,214, 5,281,745 and 5,472,925, EP 608838, Unexamined Japanese Patent Application Laid-Open Specification Nos. 10-45664, 10-57813 and 9-316023 disclose oxide catalysts which contain Mo, V, Nb and Sb (or Te) and additional elements, such as Ti, Al, W, Ta, Sn, Fe, Co and Ni.
In addition, EP 945432 A1 discloses an oxide catalyst containing Mo, V and Sb and additional elements, such as Ti, Sn, Fe, Cr, Ga, Li, Mg and Ca.
Further, U.S. Pat. Nos. 5,693,587, 5,854,172 and 5,972,833 disclose oxide catalysts which contain V and Sb and additional elements, such as Ti, Sn, Li, Mg, Na, Ca, Sr, Ba, Co and Fe.
When the oxide catalysts described in the above-mentioned publications are used for a catalytic oxidation or ammoxidation of propane or isobutane in the gaseous phase, the selectivity for the desired unsaturated carboxylic acid or unsaturated nitrile is unsatisfactory and, therefore, these oxide catalysts cannot be used for an efficient production of the desired product.
A carrier-supported catalyst (a catalyst comprising a compound having a catalytic activity and a carrier (such as silica) having supported thereon the compound) has high mechanical strength and is suitable for use in a fluidized-bed reactor. However, when a carrier-supported catalyst is prepared using the oxide catalysts disclosed in the above-mentioned publications, the selectivity for the desired products tends to be lowered. Therefore, the oxide catalysts disclosed in the above-mentioned publications have a problem in that the mode of the use of the oxide catalysts is limited.
For the reasons mentioned above, there is a strong demand for a development of an oxide catalyst which is capable of improving the selectivity for the desired products in a catalytic oxidation or ammoxidation of propane or isobutane.